Corrosion resisting coating



y 1935- c. E. HEUSSNE R CORROSION RESISTING COATING Filed May 29, 1953 'ME flLI ARTICLE.

PRO TECT/VE C'OA TING Patented i, 19, 1936 FICE .coaaosron BESISTING coarmc' Carl E. Heussner, Detroit, Mich, assignor to Chrysler Corporation, Detroit,

ration of Delaware Mich, a. corpo- Application May 29, 1933, sum No. 673,475

14 Claims.

This invention relates to an improved coating for metal articles-and to an improvedcoating bath and method of forming such coatings.

One of the main objects of the invention is to provide a corrosion resisting coating for articles which consist of or contain zinc, such as zinc I die cast parts, and particularly to provide a coating of this character which resists corrosion of such articles by halogen and/or sulphur containing salts and acids, mineral and organic acids ands the corrosive constituents of motor oils and Other objects of the invention are to provide particularly adapted for the reception of pla deposits, such as nickel and chromium, as we as for the reception of paint and enamel; to provide a coating for articles consisting of or 20 containing zinc which renders those portions of during plating, passive to the corrosive action of the plating bath; and to provide a coating of this kind. which is particularly adapted to protect those surfaces of such articles which, due to lack of throwing power of nickel plating solutions, do not receive a nickel coating, so as to prevent corrosion of such surfaces by the solution and I contamination of the solution by the corrosion reaction products.

Further objects of my invention are to provide an improved method for coating articles consisting of or containing zinc by which some of the zinc at the exposed surfaces of such articles is caused to react with ingredients of a coating forming bath in such a manner as\to form complex salts of zinc and other metalssuch as alkaline earth metals and metals selected from the group consisting of manganese and aluminum; to provide a process of this character by which the formation of such compositions is conducted at the surfaces of the varticles so as to cause the compositions to become integrally united with the articles; and to provide an improved bath for forming such protective coatings which is.

45 precipitated during operation;

The drawing is a fragmentary sectional-view of an article having my im p oved coating on one side thereof. I I

m improved corrosionresisting treatment is a coating of this character which is smooth 1313i) such articles upon which metal is not deposited.

stable and from which the contents are not particularly adapted for protecting the surfaces of. metal articles which either contain or consist of zinc but it may be used to advantage upon articles formed of other non-ferrous metals, as 55 well as ferrous metals. In'generai, the plating a proper amounts of a nitrate of an alkaline earth metal, a soluble salt of a metal selected from the group of metals consisting of manganese and aluminum, preferably a bivalent metal thereof, and an acidifying agent. The following formulas represent some of the combinations of the above materials which have been found to produce satisfactory results, the proportions set forth being variable within substantially wide limits.

1. Bariumnitrate .1........ grams Manganous carbonate 8 grams Phosphoric acid. grams 15 Water .1 litre 2. Strontium nitrate 12 grams Manganous carbonate 8 grams Phosphoric acid. 20 grams water 1 litre 2o 3. Barium nitrate .i 15 grams Manganous carbonate 8 grams Oxalic acid grams I Water 1 litre 25 4. Strontium nitratm, 12 grams Manganous carbonate 8 grams Oxalic acid 25 grams Water 1 litre 5. Barium nitrate 15 grams Manganous hydroxide 8 grams Phosphoric acid. 20 grams Water I 1 litre 6. Strontium nitrate- 12 grams Manganous hydroxide 8 grams Phosphoric acid. 20 grams Water 1 litre 7. Barium nitrate 15 grams 4o Manganous hydroxide"; 8 grams Oxalic acid. 25 grams Water' 1 .litre 8. Barium nitrate 15 grams Aluminum hydrate 10 grams Phosphoric acid 14 grams Water 1 litre From 'the foregoing formulas, it should be i understood that strontium nitrate may be used in place of-barium nitrate and that oxalic acid maybe used in place of phosphoric acid and that either manganous hydroxide or aluminum hydrate may be used in place of. manganous car-w bonate in'all of theyarious combinations. When not necessary, toadd a small amount of glucose or dextrose. The addition of /2 gram of sodium dichromate to any of the above mentioned formulas has been found'to be beneficial-in the formation of protective coatings upon articles oi various metallic compositions.

My improved protective coating forming bath is preferably contained in a lead lined tank or receptacle which is provided with steam heating coils or other heating meanscapable of maintaining the bath at a temperature of 150 to 212 F. Operation at a temperature of 200? F. or any temperature slightly below the boiling point of water is particularly efficient inasmuch as the chemical action oi. the contents of the bath upon the article treated is expedited. without excessive vaporization of the bath. The articles are preferably cleaned with any commercial' cleaning solution, water washed, and thenmoved through the bath by a conveyer which is operated in such a manner as to allow'each article to remain in the bath for from 5 to 15 minutes. When the temperature of the bath is substantially 210 F.' a 10Tminute treating period is ample to produce ato protect the coating, of sufflcient thiclmes article from corrosion.

Protective coatings iormedin accordance with my invention includecomplex salts of the metals introduced into the solution trom'whichthey are formed. "some 01' these salts comprise inorganic compounds having a metal element oLthe alkaline earth group and a metal element-of the aluminum-zinc group combined with the acid radical of phosphoric acid, oxalic acid, or J other acids, depending upon which is used as the 9,016.11 l

tying agent of the bath. when Formula -#1is employed'the, resulting coating contains zinc barium phosphate, manganous barium vphosphate, xinc-pyro phosphate, and zinc-phosphate, as wellas the phosphates oi the individual metals oi-the coatingbath; The coatings resulting from solutions havin'gvarious other compositions, set.

forth above include thevcomple'x salts and the salts. of the individual metals contained in 'the bath solution Iromwhich they are formed.

A coating formed-in accordance withmy .in--

vention upon articles containing 01'" consisting of zinc is extremely smooth and has the appearance oi vgunmetal. Such coatings iorm a-s'uitable under layer for the reception of paints varnishes,

- lacquers and "enamels; asyvell as for'the recep- I tion of metallic-plated deposits Those portions 1 bath by the corrosion reaction of articles-which are so disposed that plating is not deposited thereon due to the lack'of throwing power 'offvarious plating'solutions, 'such as nickel solutions, are protected Irom corrosion by the" action of the ;plati ng bath thereon during plating operations..- In manner fouling of the products is practicallyeliminated.

Although but several in the sequence of steps; as wellas'in the temwithout departing from the spirit of my invention, and it is not my intention to limit'itsscope' other than by the terms of the appendedclaims;

1. A bath'ior forming sauces resisting coating on articles containing .zinc'comprising a water solution substantially free from iron and its compounds including the reaction products or specific embodiments my invention .are shown, it is understood-thatvarious changesin the materials employed and barium nitrate, a water soluble manganous salt. and an acidifying agent.

2. A' bath for forming a con'osion resisting coating on zinc and its alloys comprising a water solution substantially me from iron and its compounds having a solute including the reaction I products of a nitrate'of a metal selected fromthe group of metalsconsisting of barium and strontium, a compound selected from the group of compounds consisting of manganous carbonate, manganous hydroxide and aluminum hydrateand an acid selected from the group 'of acids consisting of phosphoric acid and oxalic acid.

3, The method of forming a corrosion resisting coating -on zinc and zinc alloy articles which consists in reacting upon the zinc at thesurface of said articles a water solution substantially free from iron and its compounds into which has been introduced a nitrate of a metal selected from the group of metals consistingof barium and strontium; a compound selected irom' the group of compounds consisting of manganous carbonate, manganous hydroxide andaluminum hydrate and an acid selected from a group of acids consisting of phosphoric acidand acid. v

4. An articl'formed of metal selected'irom a group of metals consisting of zinc and zinc alloys having a coating formed thereon substantially g solution substantially free from iron and its compounds having a solutelncluding the reaction products of barium nitrate, bonate and phosphoric acid. a l

, resisting coatg ings on zinc and its alloys comprising a water 0 manganous car- 6."1 he method 01 forming a. corrosion resisting coating on zinc-and zinc alloy articles, which consists in reacting upon the zinc at the surface of said-articles a water solution subtantially tree from iron and it's'compounds into which hasbeen aded barium nitrate, manganous-carbonate and phosphoricacid. V

Fl. article formed of metal selected from a group'of metals consisting of zinc and zinc al- A loys having a coating, thereonincludinga reaction product of some.oi the zinc or said article, barium nitrate, manganous carbonate and phos- "8. A bath tor'forming corrosion resisting coatings on, zinc and. zinc-alloys comprising Witter solutionj substantiallynrreetrom iron'andits compounds having a solute including the're'action-products of a nitrate 01 a metal selected from. the, group of. metals consisting o! barium and strontium, manganous carbonate and 'an acid selected-from a group of acids consisting phosphoric acid and oxalic acid.

' tion substantiallyifree from iron and its com- 9. A bath i'orming corrosion resisting coatings on zinc, andits alloys comprising awater solu'-- pounds'having a solute including the reaction" products'oi barium nitrate, manganous nate andoxali'c acid, T

19: An article formed 91.. metal seats-anon a group of metals consisting of zlnc'and zinc'alloys having a coatingthereon includi'nga reaction product of some of the zinc of said article, barlum nitrate, manganous carbonate and oxalic acid.

11. The method of forming a corrosion resisting coating on zinc and zinc alloy articles, which consists in reacting upon the zinc at the surface of said articles a water solution substantially free'from iron and its compounds into which has been'added barium nitrate, manganous carbonate and oxalic acid.

I 12. A bath for. forming corrosion resisting coatings on zinc and its alloys comprising a action products of barium nitrate, aluminum hy-- drate and phosphoric acid.

13. An article formed 01' metal selected from a group of metals consisting of zinc and zinc alloys having a coating thereon including a reaction product or some 01' the zinc 01' said article, barium nitrate, aluminum hydrate and phosphoric acid.

14. The method of forming a corrosion resisting coating on zinc and zinc alloy articles, which consists in reacting upon the zinc at the surface of said articles a water solution substantially free from iron and its compounds into which has been added barium nitrate, aluminum hydrate and phosphoric acid.

CARL E. HEUSSNER. l5 

